The verbs of the strong conjugation..form the past tense by a change of the root-vowel.
出自: Richard MorrisHer grammar..included a highly personal conjugation of the verb to be.
出自: V. S. Naipaul"the casual couplings of adolescents"
"the mating of some species occurs only in the spring"
"the union of opposing factions"
"he looked forward to the unification of his family for the holidays"